1. Field of the Invention
The present invention relates to a color cathode ray tube, and more particularly, to a panel and shadow mask of a color cathode ray tube having a curvature and a radius of curvature for forming a screen.
2. Background of the Related Art
The cathode ray tube is an important component of a display, such as a TV receiver or a computer monitor, for displaying an image. FIG. 1 illustrates a side view of such a color cathode ray tube, with a partial cut away view.
Referring to FIG. 1, there is a panel 1 having an inside surface a fluorescent film 2 is formed thereon in a front portion of the color cathode, and a funnel 3 welded to a rear of the panel 1 with frit glass. There is a shadow mask 6 fitted close to an inside of the panel 1 in a state the shadow mask 6 is fixed to a frame 7 for selection of colors of electron beams emitted from an electron gun 4, and an electron gun 4 provided inside of a neck portion 3a of the funnel 3. The frame 7 is fastened to the panel 1 as the frame is hung from a sidewall of the panel 1 by support springs 8 fixed to the frame 7 and inserted in stud pins 9 fixed to the sidewall of the panel 1. There is an inner shield 10 fastened to one side of the frame 7 by fastening springs 11 for protecting the electron beams 5 moving toward the fluorescent film 2 from an external geomagnetism. There is a deflection yoke 13 having a plurality of poles attached to an outer circumference of the neck portion 3a for correcting a path of travel of the electron beams 5 so that the electron beams 5 hit onto a required fluorescent material exactly, and a reinforcing band 12 strapped around an outer circumference of the cathode ray tube for preventing breakage of the cathode ray tube from an external impact during operation of the cathode ray tube. Within the foregoing basic structure of the cathode ray tube, the shadow mask 6 is formed to have a curvature, and disposed to have a gap to the panel 1, to form a panel assembly together with the panel, for reproducing a picture as the three electron beams 5 emitted from the electron gun 4 hit the fluorescent material on an inside surface of the panel 1, exactly. Therefore, in order to form the picture, an accurate curvature design of the shadow mask 6 is required, when a panel inside surface curvature and a grouping rate are taken into consideration as curvature design condition.
FIG. 2 illustrates a longitudinal section of a panel assembly, referring to which the panel inside surface curvature and the grouping rate will be explained in more detail.
When Rp denotes an inside surface radius of curvature of the panel 1, and Rm denotes a radius of curvature of the shadow mask 6, basically the radius of curvature Rm of the shadow mask 6 is set to have a fixed ratio to the inside surface radius of curvature Rp of the panel 1. According to this, once the inside surface radius Rp of curvature of the panel 1 is given, the radius Rm of curvature of the mask 6 is dependent on the inside surface radius Rp of curvature of the panel. Along with such a linear dependency on the panel inside surface radius of curvature, the shadow mask 6 is designed, taking a Grouping Rate(G/R), a configuration of the electron beams which fixes a color purity of the picture, into consideration, which can be expressed as an equation, below.             G      /      R        =                  3        xc3x97        S        xc3x97        Q                    Ph        xc3x97        L              ,
where,
S: a distance between a deflection center and an electron beam center
Q: a distance between a slot in a shadow mask to an inside surface of the panel
Ph: a distance between centers of slots in the shadow mask
L: a distance from a center of deflection of the electron beam to an inside surface of the panel.
In general, the G/R is set to be G/R=1.000, so that the electron beams exactly hit a required fluorescent material throughout an effective surface of the shadow mask 6, for enhancing the color purity. Thus, in general the curvature and the radius Rm of curvature of the shadow mask 6 is designed to be dependent on the inside surface curvature of the panel basically, and to maintain the G/R constant for securing a color purity.
In the meantime, recently the inside surface radius Rp of curvature of the panel is increased since a wedge ratio, a ratio of a center thickness to a corner thickness of the panel, is limited to a certain range owing to a limitation in formation while an outer surface of the panel 1 is planarized for providing a flat picture, with a consequential increase of the radius of curvature of the shadow mask 6. Since such a shadow mask 6 is weak in strength, the shadow mask 6 is susceptible to deformation caused by an external physical force during handling the shadow mask 6, or howling caused by an impact or a speaker sound during operation of the cathode ray tube. The howling, dependent on vibration characteristics of the shadow mask, occurs when external acoustic wave or vibration is reached to the shadow mask 6, which deteriorates a color reproducibility, to change picture colors in a screen, partly. The shadow mask of the related art panel is compared to the shadow mask of the present invention, such that an extent of deterioration of the howling characteristics is more serious than the deterioration of strength of the shadow mask.
For solving such problems, various methods are employed, which can be summarized as follows.
First, a rigidity of the frame 7 itself is enhanced either by changing a form of the springs 11 which support the frame 7, or by providing a curve to the frame 7. However, since this change to the frame 7 is not improvement to the shadow mask 6 itself which affects the howling the most sensitively and directly, this change can not be any fundamental solution. Moreover, the improvement to the spring 11 and the frame 7 form are not effective to the flat cathode ray tube.
Second, as shown in FIG. 3, a bead 14 having a curvature different from an overall curvature is applied within the effective surface of the shadow mask 6. However, since the bead 14 is within the effective surface, the bead 14 causes difficulty in coating the fluorescent material on the inside surface of the panel 1 in fabrication of the cathode ray tube and a local non-uniformity of the fluorescent surface, that, not only gives inconvenience in view, but also deforms the picture. By the way, the bead 14 in the effective surface enhances a strength of the shadow mask 6 relatively, but shows a limitation in improvement of the howling.
Fourth, as shown in FIG. 4, the shadow mask 6 is pre-tensioned in fitting to the frame 7, and slightly pre-tensioned wire dampers 15 are strapped on the shadow mask 6. However, this method has difficulty in that there should be no deformation in fitting the pre-tensioned shadow mask 6 to the frame 7, and the damper wire 15 should be strapped to exert a uniform pressure throughout the pre-tensioned shadow mask 6, that makes a fabrication process complicate, with an increased production cost.
Alike the bead 14 application, though the damper wire 15 application is favorable in view of strength of the shadow mask 6, the applications have a certain limit in a vibration attenuation.
As shown, because the related art methods in which separate structural bodies are used can not solve the problems, improvements to the panel or shadow mask itself are required. That is, either a method for improving a curvature of the inside surface of the panel, which fixes the curvature of the shadow mask, or separate from this, a method for designing a curvature of the shadow mask itself separate from the curvature of the inside surface of the panel is required.
Accordingly, the present invention is directed to a color cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a color cathode ray tube which can prevent deterioration of a color reproducibility caused by an impact or speaker sound during operation of the cathode ray tube owing to improvement of the howling characteristics.
An object of the present invention is to provide a color cathode ray tube which has an improved structural strength for preventing deformation caused by an external force.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the color cathode ray tube includes a panel in front portion of the cathode ray tube, and a shadow mask spaced from, and fitted to rear of the panel for selecting a color from electron beams, wherein at least one of an inside surface of the panel and the shadow mask have a curvature structure in which a radius of curvature varies continuously within a fixed ratio range.
The variation of radius of curvature of the inside surface of the panel satisfies the following equation.
Rpi less than Rpixe2x88x921 (i=1, . . . , n)       Rpi     greater than                                         Rpn            -            Rp0                    Lpn                ⁢        Lpi            +      Rp0        ,      (                  when        ⁢                  xe2x80x83                ⁢        i            ≠              n        ⁢                  xe2x80x83                ⁢        or        ⁢                  xe2x80x83                ⁢        0              )    ,
if i=n, Rpi=Rpn, and if i=0, Rpi=Rp0, where,
Rp0 denotes a radius of curvature at a center of the inside surface of the panel,
Rpi denotes a radius of curvature at any location on the inside surface of the panel,
Rpn denotes a radius of curvature at an end of effective surface on the inside surface of the panel,
Lpi denotes a distance from a center of the inside surface of the panel to any location on the inside surface of the panel, and
Lpn denotes a distance from a center of the inside surface of the panel to an end of an effective surface, and
the variation of radius of curvature of the shadow mask satisfies the following equation.
Rmi less than Rmixe2x88x921 (i=1, . . . , n)       Rmi     greater than                                         Rmn            -            Rm0                    Lmn                ⁢        Lmi            +      Rm0        ,      (                  when        ⁢                  xe2x80x83                ⁢        i            ≠              n        ⁢                  xe2x80x83                ⁢        or        ⁢                  xe2x80x83                ⁢        0              )    ,
if i=n, Rmi=Rmn, and if i=0, Rmi=Rm0, where,
Rm0 denotes a radius of curvature at a center of the shadow mask,
Rmi denotes a radius of curvature at any location on the shadow mask,
Rmn denotes a radius of curvature at an end of effective surface on the shadow mask,
Lmi denotes a distance from a center of the shadow mask to any location on the shadow mask, and
Lmn denotes a distance from a center of the shadow mask to an end of an effective surface.
The curvature structures of the inside surface of the panel and the shadow mask can be expressed as Rpi=xcex3p(Lpi)Rp0 and Rmi=xcex3m(Lmi)Rm0 respectively, where the xcex3p and xcex3m denote functions dependent on distances Lpi and Lmi respectively, and the proportional functions xcex3p(Lpi) and xcex3m(Lmi) are continuously decreasing functions with respect to variables Tpi and Tmi which are proportional to the distances Lpi and Lmi according to coefficients xcex1p and xcex1m to establish the following equations, respectively.
xcex3p(Lpi)=cos(Tpi), (Tpi=xcex1pLpi), xcex3p(Lpi)=cos(xcex1pLpi), and xcex3m(Lmi)=cos(Tmi), (Tmi=xcex1mLmi), xcex3m(Lmi)=cos(xcex1mLmi).
The curvature structures are formed up to points Lp80% and Lm80% 80% of distances from the centers of the inside surface of the panel and the shadow mask to the ends of the effective surfaces respectively, for improving howling.
The proportional functions xcex3p and xcex1m have values in ranges of 0.75xcx9c0.97 and 0.65xcx9c0.97 at the 80% points Lp80% and Lm80% respectively, and the coefficients xcex1p and xcex3m have values expressed by the following inequalities depending on ranges of values of the proportional functions xcex3p and xcex3m at the 80% points Lp80% and Lm80% respectively.                               cos                      -            1                          ⁢                  (          0.97          )                            L                  m          ⁢                      xe2x80x83                    ⁢          80          ⁢                      xe2x80x83                    ⁢          %                       less than =          α      m         less than =                            cos                      -            1                          ⁢                  (          0.75          )                            L                  m          ⁢                      xe2x80x83                    ⁢          80          ⁢                      xe2x80x83                    ⁢          %                                                  cos                      -            1                          ⁢                  (          0.97          )                            L                  p          ⁢                      xe2x80x83                    ⁢          80          ⁢                      xe2x80x83                    ⁢          %                       less than =          α      p         less than =                            cos                      -            1                          ⁢                  (          0.75          )                            L                  p          ⁢                      xe2x80x83                    ⁢          80          ⁢                      xe2x80x83                    ⁢          %                    
Preferably, the curvature structures are true in at least one of a long axis (X-axis), a short axis (Y-axis), and a diagonal axis (D-axis) respectively, and more preferably in all of a long axis (X-axis), a short axis (Y-axis), and a diagonal axis (D-axis). Additionally, it is more preferable that the curvature structures are true in all directions contained between the long axis (X-axis), the short axis (Y-axis), and the diagonal axis (D-axis).
The foregoing curvature structure is applicable to the inside surface of the panel of a color cathode ray tube of the present invention, and, separate from it, also applicable to a shadow mask independently. Or the curvature structure is applicable both to the inside surface of the panel and the shadow mask.
The present invention enhances a strength, and improves howling of the shadow mask, to minimize deformation of the shadow mask and prevent deterioration of the color reproducibility.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.